Biopolymers may be used for therapeutic or non-therapeutic purposes. Biopolymer-based therapeutics, such as antibody or enzyme formulations, are widely used in treating disease. Non-therapeutic biopolymers, such as enzymes, peptides, and structural proteins, have utility in non-therapeutic applications such as household, nutrition, commercial, and industrial uses.
Biopolymers used in therapeutic applications must be formulated to permit their introduction into the body for treatment of disease. For example, it is advantageous to deliver antibody and protein/peptide biopolymer formulations by subcutaneous (SC) or intramuscular (IM) routes under certain circumstances, instead of administering these formulations by intravenous (IV) injections. In order to achieve better patient compliance and comfort with SC or IM injection though, the liquid volume in the syringe is typically limited to 2 to 3 ccs and the viscosity of the formulation is typically lower than about 20 centipoise (cP) so that the formulation can be delivered using conventional medical devices and small-bore needles. These delivery parameters do not always fit well with the dosage requirements for the formulations being delivered.
Antibodies, for example, may need to be delivered at high dose levels to exert their intended therapeutic effect. Using a restricted liquid volume to deliver a high dose level of an antibody formulation can require a high concentration of the antibody in the delivery vehicle, sometimes exceeding a level of 150 mg/mL. At this dosage level, the viscosity-versus-concentration plots of the formulations lie beyond their linear-nonlinear transition, such that the viscosity of the formulation rises dramatically with increasing concentration. Increased viscosity, however, is not compatible with standard SC or IM delivery systems.
As an additional concern, solutions of biopolymer-based therapeutics are also prone to stability problems, such as precipitation, fragmentation, oxidation, deamidation, hazing, opalescence, denaturing, and gel formation, reversible or irreversible aggregation. The stability problems limit the shelf life of the solutions or require special handling.
As an example, one approach to producing protein formulations for injection is to transform the therapeutic protein solution into a powder that can be reconstituted to form a suspension suitable for SC or IM delivery. Lyophilization is a standard technique to produce protein powders. Freeze-drying, spray drying and even precipitation followed by super-critical-fluid extraction have been used to generate protein powders for subsequent reconstitution. Powdered suspensions are low in viscosity before re-dissolution (compared to solutions at the same overall dose) and thus may be suitable for SC or IM injection, provided the particles are sufficiently small to fit through the needle. However, protein crystals that are present in the powder have the inherent risk of triggering immune response. The uncertain protein stability/activity following re-dissolution poses further concerns. There remains a need in the art for techniques to produce low viscosity protein formulations for therapeutic purposes while avoiding the limitations introduced by protein powder suspensions.
In addition to the therapeutic applications of proteins described above, biopolymers such as enzymes, peptides, and structural proteins can be used in non-therapeutic applications. These non-therapeutic biopolymers can be produced from a number of different pathways, for example, derived from plant sources, animal sources, or produced from cell cultures.
The non-therapeutic proteins can be produced, transported, stored, and handled as a granular or powdered material or as a solution or dispersion, usually in water. The biopolymers for non-therapeutic applications can be globular or fibrous proteins, and certain forms of these materials can have limited solubility in water or exhibit high viscosity upon dissolution. These solution properties can present challenges to the formulation, handling, storage, pumping, and performance of the non-therapeutic materials, so there is a need for methods to reduce viscosity and improve solubility and stability of non-therapeutic protein solutions.
Proteins are complex biopolymers, each with a uniquely folded 3-D structure and surface energy map (hydrophobic/hydrophilic regions and charges). In concentrated protein solutions, these macromolecules may strongly interact and even inter-lock in complicated ways, depending on their exact shape and surface energy distribution. “Hot-spots” for strong specific interactions lead to protein clustering, increasing solution viscosity. To address these concerns, a number of excipient compounds are used in biotherapeutic formulations, aiming to reduce solution viscosity by impeding localized interactions and clustering. These efforts are individually tailored, often empirically, sometimes guided by in silico simulations. Combinations of excipient compounds may be provided, but optimizing such combinations again must progress empirically and on a case-by case basis.
There remains a need in the art for a truly universal approach to reducing viscosity in protein formulations at a given concentration under nonlinear conditions. There is an additional need in the art to achieve this viscosity reduction while preserving the activity of the protein and avoiding stability problems. It would be further desirable to adapt the viscosity-reduction system to use with formulations having tunable and sustained release profiles, and to use with formulations adapted for depot injection.